The cerebral arterial waveform illustrates a very interesting point in fetal physiology. When the fetus is hypoxic, the cerebral arteries tend to become dilated in order to preserve the blood flow to the brain. The systolic to diastolic (A/B) ratio will decrease (due to an increase in diastolic flow) in the presence of chronic hypoxic insult to the fetus. The waveform becomes ' fattened ' and act as a sign for further obstetric intervention.

The middle cerebral artery flow velocity waveform in a fetus with growth retardation at 28 weeks.